A round 10, that is typically launched from a barrel of a weapon, consists of a cartridge case 20, a body 30 and a nose cone 40 being arranged in this order along a longitudinal axis 12, as shown in FIG. 1. A fuze (not shown), housed inside the nose cone 40, is a safety device that ensures that the projectile is safe until it has been propelled a predetermined distance away from the muzzle of the barrel; in other words, the projectile is armed only after it has been propelled over a minimum safe muzzle distance. A conventional mechanical fuze is now exemplified: once the projectile is propelled through the barrel, a spin-activated lock releases an unbalanced rotor. Rate of rotation of the rotor is regulated by a pinion assembly and a verge assembly so that after a predetermined delay time and the projectile has reached a tactical distance, the rotor is rotated into its armed position and a stab detonator on the rotor becomes aligned with a point detonating (PD) pin. Once armed, the rotor remains held in this armed position by an arming lock pin. When the nose cone strikes a target at a designed or optimum angle, ie. during such point impact mode, impact forces thrust a safe-and-arm assembly unit, on which the rotor is attached, forward and the PD pin then sets off the stab detonator. The stab detonator may in turn set off a booster 32 and/or an explosive charge 34 disposed inside the body of the projectile.
In some projectiles, there is a mechanical self-destruct mechanism disposed between the safe-and-arm assembly unit and nose cone. The mechanical self-destruct mechanism is a second safety device for setting off the stab detonator after the projectile misses its target, lands on soft ground or lands on a ground at a glazing angle and comes to rest very slowly. A mechanical self-destruct feature may use a spin-decay mechanism to release a spring loaded self-destruct (SD) firing pin onto the stab detonator after the projectile failed to explode by point impact. Applicant's own spin-decay self-destruct fuze is described in U.S. Pat. No. 6,237,495.
The above point impact detonation (PD) and self-destruct (SD) mechanisms require precise movements of mechanical parts. Sometimes, projectiles impact targets at oblique angles; this is often encountered in urban terrains; oblique target surfaces are also encountered with armoured vehicles which are specially designed with body plates arranged at some angles. Impacts at oblique angles can often damage the PD and/or SD mechanisms. As suggested in “Weapon Effect_MOUT_B0386” by the US Military Operations On Urbanized Terrain (MOUT), about 25% of projectiles used in urban terrains are rendered inoperative. Unexploded projectiles pose a hazard and thus it becomes a requirement that newly developed explosive ordnance devices have self-destruct functionality.
In an approach, U.S. Pat. No. 7,729,205, assigned to Action Manufacturing Company, describes a low current micro-controller circuit for use on a projectile. It also describes a system for accurate timing of a fuze circuit.
It can thus be seen that there exists a need for a new fuze system of high reliability to ensure that most projectiles after being deployed are exploded, either by impact and/or by self-destruct triggering.